Bennett—Rhamphorhynchus wings
dactylopatagium. Behind WP2 and 3 the strips seem to be quite long and straight,whereas they are shorter behindWP1 because of their more anteroposterior orientation. At mid-chord behindWP2 and 3, the strips seemto be best developed and evenly spaced at ~5 per mm, whereas close to the wing phalanges and in the more medial parts of the dactylopatagium posterior to WP1 they are more closelyspacedand often difficult to follow. The strips are generally not visible where the retrophalangeal wedge is present, though as noted above there appear to be a few visible within the area of the wedge impression behindWP2 and 3. In addition, the strips fade away within ~5–10mm of the trailing edge of the dactylopatagium and ~3–5 cm of the wingtip. Mapping the raised strips was difficult because they are
poorly defined and faint in many places, and so it was often necessary to arbitrarily decide whether an apparent gap in a raised longitudinal strip resulted from poor preservation of a continuous strip or from one strip ending and another beginning. Several strips seemed to extend continuously from the posterior margin of the retrophalangeal wedge until fading out near the trailing edge, a distance of ~125mm. The strips are quite straight, though there are occasional jogs to one side or another. The strips do not branch, but their number is increased by intercalation; the spacing between two adjacent strips increasing until a third strip appears midway between the two. Where best developed, the raised longitudinal strips have a
roughly symmetrical cross-section somewhat raised above the surrounding impression, corresponding to the interpretations of previous authors of the strips as positive impressions of subcylindical fibers. However, in places the shape of the strips is asymmetrical, approximating the appearance of a lapstrake or clinker-built boat hull with the raised longitudinal strips forming the exposed angles of the strakes such that the overall appearance of the impression is that of negative impressions of closely spaced broad flat structures arranged en echelon rather
853
than that of widely spaced narrow raised strips. In support of this appearance, there is a small fragment of what appears to be calcite adhering to a groove between two raised longitudinal strips ~1mm behind a small fold and ~10mm behind a point about one-third along WP3 (Fig. 4). The fragment is 2.6mm long and ~0.17mm wide. Its sides are parallel, its width corresponds well to that of the groove in which it is preserved, and its ends are fractured irregularly suggesting that it represents but a section of a longer structure. Its thickness cannot be measured, but it appears to be less than half its width, thus <0.08mm. Its superior surface resembles a gabled roof with a median ridge flanked by sloping surfaces extending to the sides of the fragment. It is argued below that the calcitic fragment is a short section of an actinofibril preserved by permineralization or replacement by calcite. The raised longitudinal strips along Fold Lines C and D
seem to be smaller and more closely spaced than generally elsewhere on the dactylopatagium. In addition, part of Fold C is not parallel to, but rather lies at a low angle to, most of the adjacent raised longitudinal strips, whereas a few smaller and more closely spaced strips follow exactly along the fold. Thus that part of the fold line appears to cut across the general pattern of raised longitudinal strips. In addition, along FoldD the raised longitudinal strips posteromedial to the fold seem to converge on the fold line slightly. Note that Zittel (1882, p. 53) stated that some raised
longitudinal strips were more prominent than the rest, marked by reddish brown iron oxide deposits, and resembled ossified tendons. Based on my examinations, no raised strips are significantly larger than the others and Zittel probably was referring to the prominent folds discussed above.
Retrophalangeal wedge.—The trace of the retrophalangeal wedge extends along the posterior side of the wing spar from a
Figure 4. Zittel wing of Rhamphorhynchus muensteri, BSP 1880 II 8. (1) Stereo pair of photographs of the fragment of actinofibril preserved by calcite within a groove forming a negative impression of the actinofibril; (2) interpretive drawing with raised longitudinal strips indicated by thin black lines, Fold E shaded medium gray, and the actinofibril fragment shaded dark gray. Abbreviations: af, actinofibril fragment preserved by calcite;; gr, groove; rls, raised longitudinal strip. Scale bar represents 0.1mm.
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